Developing electrode contamination prevention system for electrophotography

Abstract

A photoconductive drum has an image portion and a non-image portion. A biasing voltage is applied to a developing electrode when the image portion of the drum is adjacent thereto. The developing electrode is grounded when the non-image portion of the drum is adjacent thereto to prevent toner particles from being attracted thereto to accumulate and contaminate the developing electrode. A low voltage is applied to the non-image portion of the drum to remove toner from the developing electrode which was attracted thereto during development of the image portion of the drum.

What is claimed is: 
     
       1. In an electrophotographic process in which a photoconductive member having an image portion and a non-image portion is moved relative to a developing electrode, the steps of: a. applying a bias voltage to the developing electrode when the image portion of the photoconductive member is adjacent to the developing electrode;   b. charging the non-image portion of the photoconductive member to a voltage which is substantially equal to a voltage of a background portion of the image portion of the photoconductive member; and   c. grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.   
     
     
       2. In an electrophotographic process in which a photoconductive member having an image portion and a non-image portion is moved relative to a developing electrode, the steps of: a. applying a bias voltage to the developing electrode when the image portion of the photoconductive member is adjacent to the developing electrode;   b. charging the non-image portion of the photoconductive member to a voltage which is higher than a voltage of a background portion of the image portion of the photoconductive member;   c. radiating the non-image portion with light to cause the photoconductive member to conduct and reduce the voltage of the non-image portion to the voltage of the background portion of the image portion of the photoconductive member; and   d. grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.   
     
     
       3. In an electrophotographic process in which a photoconductive member having an image portion and a non-image portion is moved relative to a developing electrode, the steps of: a. electrically insulating the developing electrode from ground so that the developing electrode is self-biased by the photoconductive member;   b. charging the non-image portion of the photoconductive member to a voltage which is substantially equal to a voltage of a background portion of the image portion of the photoconductive member; and   c. grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.   
     
     
       4. In an electrophotographic process in which a photoconductive member having an image portion and a non-image portion is moved relative to a developing electrode, the steps of: a. electrically insulating the developing electrode from ground so that the developing electrode is self-biased by the photoconductive member;   b. charging the non-image portion of the photoconductive member to a voltage which is higher than a voltage of a background portion of the image portion of the photoconductive member;   c. radiating the non-image portion with light to cause the photoconductive member to conduct and reduce the voltage of the non-image portion to the voltage of the background portion of the image portion of the photoconductive member; and   d. grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.   
     
     
       5. In an electrophotographic apparatus having a photoconductive member with an image portion and a non-image portion and a developing electrode, the photoconductive member being movable relative to the developing electrode, the combination comprising: first means for electrically biasing the developing electrode when the image portion of the photoconductive member is adjacent to the developing electrode;   second means for charging the non-image portion of the photoconductive member to a voltage which is substantially equal to a voltage of a background portion of the image portion of the photoconductive member; and   third means for grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.   
     
     
       6. The apparatus according to claim 5, further comprising imaging means to radiate a light image on the image portion of the photoconductive member. 
     
     
       7. The apparatus according to claim 5, further comprising control means responsive to the movement of the photoconductive member and connected to control the first and third means. 
     
     
       8. The apparatus according to claim 5, in which the control means comprises a switch which is actuated when a leading edge of the image portion of the photoconductive member is adjacent to the developing electrode and a timer actuated by the switch, the timer being set for a time interval required for a trailing edge of the image portion of the photoconductive member to be moved adjacent to the developing electrode. 
     
     
       9. The apparatus according to claim 8, in which the switch is a reed switch. 
     
     
       10. In a electrophotographic apparatus having a photoconductive member with an image portion and a non-image portion and a developing electrode, the photoconductive member being movable relative to the developing electrode, the combination comprising: first means for electrically biasing the developing electrode when the image portion of the photoconductive member is adjacent to the developing electrode;   second means for charging the non-image portion of the photoconductive member to a voltage which is higher than a voltage of a background portion of the image portion of the photoconductive member;   third means for radiating the non-image portion with light to cause the photoconductive member to conduct and reduce the voltage of the non-image portion to the voltage of the background portion of the image portion of the photoconductive member; and   fourth means for grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.   
     
     
       11. The apparatus according to claim 10, in which the second means is further operative to charge the image portion of the photoconductive member to the voltage which is higher than the voltage of the background portion of the image portion of the photoconductive member. 
     
     
       12. The apparatus according to claim 11, in which the third means is further operative to radiate light on the image portion of the photoconductive member prior to charging by the second means. 
     
     
       13. The apparatus according to claim 10, further comprising a movable shutter disposed between the third means and the photoconductive member. 
     
     
       14. The apparatus according to claim 10, further comprising imaging means to radiate a light on the image portion of the photoconductive member. 
     
     
       15. The apparatus according to claim 10, further comprising control means responsive to the movement of the photoconductive member and connected to control the first and fourth means. 
     
     
       16. The apparatus according to claim 15, in which the control means comprises a switch which is actuated when a leading edge of the image portion of the photoconductive member is adjacent to the developing electrode and a timer actuated by the switch, the timer being set for a time interval required for a trailing edge of the image portion of the photoconductive member to be moved adjacent to the developing electrode. 
     
     
       17. The apparatus according to claim 16, in which the switch is a reed switch. 
     
     
       18. In an electrophotographic apparatus having a photoconductive member with an image portion and a non-image portion and a developing electrode, the photoconductive member being movable relative to the developing electrode, the combination comprising: first means for electrically insulating the developing electrode from ground so that the developing electrode is self-biased by the photoconductive member;   second means for charging the non-image portion of the photoconductive member to a voltage which is substantially equal to a voltage of a background portion of the image portion of the photoconductive member; and   third means for grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.   
     
     
       19. In an electrophotographic apparatus having a photoconductive member with an image portion and a non-image portion and a developing electrode, the photoconductive member being movable relative to the developing electrode, the combination comprising: first means for electrically insulating the developing electrode from ground so that the developing electrode is self-biased by the photoconductive member;   second means for charging the non-image portion of the photoconductive member to a voltage which is higher than a voltage of a background portion of the image portion of the photoconductive member;   third means for radiating the non-image portion with light to cause the photoconductive member to conduct and reduce the voltage of the non-image portion to the voltage of the background portion of the image portion of the photoconductive member; and   fourth means for grounding the developing electrode when the non-image portion of the photoconductive member is adjacent to the developing electrode.